Machines having a moving, inclined forming wire are known for making nonwoven mats from fibers and it is known to use such a machine as manufactured by Voith GmBh and Sandy Hill Corp. for nonwoven mats as substrates in the manufacture of a large number of products and also as a facing for products like wallboard, foam board and insulation. Methods of making nonwoven mats by wet laid processes are described in U.S. Pat. Nos. 4,112,174, 4,681,802 and 4,810,576, the disclosures of which are hereby incorporated herein by reference. In these processes a slurry of glass fiber is made by adding fiber to a typical white water in a pulper to disperse the fiber in the white water forming a slurry having a very low fiber concentration to feed to the above machines where the fibers are deposited on the moving forming wire to form a wet web. The wet, nonwoven web of fiber is then transferred to a second moving screen in-line with the forming screen and run through a binder saturating station where an aqueous binder mixture, such as an aqueous urea formaldehyde (UF) resin based binder mixture, is applied to the mat in any one of several known ways. The mat, saturated with the binder, is then run over a suction section while still on the second moving screen to remove excess binder.
The wet mat is then transferred to a moving wire mesh belt, or a honeycomb drum, and run through an oven to dry the wet mat and to cure (polymerize) the UF based resin binder to bond the fibers together in the mat. Preferably, the aqueous binder solution is applied using a curtain coater or a dip and squeeze applicator, but other methods of application such as spraying are also known.
In the drying and curing oven the mat is subjected to temperatures up to 450 or even 550 degrees F. or higher for periods usually not exceeding 1-2 minutes and as little as a few seconds. Alternative forming methods for nonwoven fiber mats include the use of well known processes of cylinder forming, continuous strand mat forming which lays continuous strands of glass fibers in overlapping swirls, and “dry laying” using carding or random fiber distribution.
The fastest and widest of the wet forming machines described above use a very large pump to feed the fibrous slurry to the forming box because of the high degree of dilution needed to keep the fibers well dispersed and to achieve the degree of uniformity of fibrous structure needed for the end use of the nonwoven mats. On existing machines, the productivity of the mat line is being limited by the size of the pump available, and the practicality of larger pumps for this purpose. If a higher feed rate of the dilute aqueous slurry to the forming box could be achieved reasonably, the productivity of the mat line could be increased substantially producing a significantly lower fixed cost per capacity unit and also a significantly lower direct cost per capacity unit. Also, since much of the market for nonwoven mats, roofing, is very seasonal and inventory is relatively low density and very bulky, an increased mat capacity per line, per crew, per location, etc. would also provide a significant competitive advantage during the peak demand times.
Wet forming machines having two or more separate forming systems with separate forming boxes are also known and it is known to use such machines to make multilayer, nonwoven mats. In such machines, one layer is formed on the moving, inclined wire, and then a second layer, of a different composition, is formed on top of the first layer with the first layer being exposed to the air for a very short time. Multilayer mat made on such machines have a clear line of demarcation between the layers and this can lead to delamination and other shortcomings. It is known in U.S. Pat. No. 3,778,341, to “piggyback” two forming boxes such that the first layer is not exposed to the air before a second layer is formed against the first layer, but there is still a clear line of demarcation between the two layers.
It is now known as shown in U.S. Pat. No. 6,761,801, to make a forming box having one or more separators therein, each separator called a lamella. The lamella can be made of a flexible polymer membrane and doesn't extend all the way to the moving forming wire. A separate, dilute particulate and/or fibrous aqueous slurry can be fed to each section of the forming box using separate feed pipes and headers. In such machines there is some blending of the two separate slurries at the interface before reaching the forming wire such that there is not such a clear line of demarcation between the layers as the multilayer mats described in the previous paragraph. However, such a machine is known for use only in making paper, tissue or cardboard.